The self-diffusion of neat water, dimethyl sulfoxide (DMSO), octanol, and the molecular components in a water-DMSO solution was measured by H-1 and H-2 NMR diffusion experiments for those fluids imbibed into controlled pore glasses (CPG). Their highly interconnected structure is scaled by pore size and shows invariant pore topology independent of the size. The nominal pore diameter of the explored CPGs varied from 7.5 to 72.9 nm. Hence, the about micrometer mean-square diffusional displacement during the explored diffusion tithes was much larger than the individual pore size, and the experiment yielded the average diffusion coefficient Great care was taken to establish the actual pore: volumes of the CPGs. Transverse relaxation experiments processed by inverse Laplace transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore size for the larger pores and becomes stronger toward the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes, while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. Deviation from the trends predicted by the Renkin equation indicates that the interaction with the pore wall is not a just simple steric one but is in part dependent on the specific features of the molecules explored here.

The self-diffusion of neat water, dimethylsulfoxide (DMSO), octanol and the molecular components in a water-DMSO solution were measured by 1H and 2H NMR diffusion experiments for those fluids imbibed into Controlled Pore Glasses (CPG). Their highly interconnected structure is scaled by pore size and shows the some pore topology independently of the size. The nominal pore diameter of the explored CPGs varied from 7.5 nm to 72.9 nm. Hence, the ∼μm mean-square diffusional displacement during the explored diffusion times was much larger than the individual pore size. Great care was taken to establish the actual pore volumes of the CPGs. In addition, transverse relaxation experiments processed by Inverse Laplace Transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore sizes for the larger pores and becomes larger towards the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. The interaction with the pore wall is not just simple steric one but must in part be dependent on the specific features of the molecules explored here.

At BAM, which is the federal institute for materials research and testing in Germany, it is one of our tasks to evaluate the safety of casks designed for transport and/or storage of radioactive material. This includes the assessment of the service lifetime of elastomeric seals that are part of the container lid system with regard to the requirements for long-term safety (40 years and more) of the containers. Therefore, we started an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) which are aged at four different temperatures (75 degrees C, 100 degrees C, 125 degrees C and 150 degrees C) up to 1.5 years. In order to assess sealability, O-rings are aged in compression by 25% (corresponding to the compression during service) between plates as well as in flanges that allow leakage rate measurements. For comparison, uncompressed O-rings are aged as well. Further methods characterising seal performance are compression stress relaxation (CSR) reflecting the loss of sealing force of a compressed seal over time, and compression set (CS) which represents the recovery behaviour of a seal after release from compression. Additionally, hardness is measured for information about the change of mechanical properties. The experimental results indicate that while hardness, CSR and CS show considerable degradation effects, the leakage rate stays relatively constant or even decreases until shrinkage combined with the loss of resilience of the aged seal leads to leakage. This demonstrates that static leakage rate, which is the only available direct seal performance criterion, has only limited sensitivity towards the degradation of the seal material. CS data is extrapolated using time-temperature shifts and Arrhenius graphs. An exemplary CS of 50% would be reached after approx. 1.2, 17 and 29 years at 60 degrees C for HNBR, EPDM and FKM respectively.

The causes of changes in dielectric response as a result of thermal and irradiative ageing of cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler were investigated. Samples were aged in three different combinations of irradiation dose rate and temperature, 0.42 kGy h(-1) at 85 degrees C, and 1.58 kGy h(-1) at 55 and 85 degrees C, and subsequently studied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer, and tensile testing. The extractable mass fraction and density were determined and related to the imaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in the dielectric permittivity, stiffness, density and degree of oxidation, together with a decrease in both strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for the strain-at-break, the properties changed in a linear fashion with increasing imaginary part of the dielectric permittivity at 100 kHz, with particularly good agreement with respect to the density. As these properties are affected by the degree of oxidation, the results show that both NMR using a portable spectrometer and dielectric spectroscopy can be used as condition monitoring techniques to detect the degree of oxidation in complex systems such as filled copolymers.

The causes of changes in dielectric response as a result of thermal and irradiative ageingof a cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler wereinvestigated. Samples were aged in three different combinations of irradiation dose rate andtemperature, 0.42 kGy h–1 at 85 °C, and 1.58 kGy h–1 at 55 and 85 °C, and subsequentlystudied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer andtensile testing. The extractable mass fraction and density were determined, and related to theimaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in thedielectric permittivity, stiffness, density and degree of oxidation, together with a decrease inboth strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for thestrain-at-break, the properties changed in a linear fashion with increasing imaginary part ofthe dielectric permittivity at 100 kHz, with a particularly good agreement with respect to thedensity. As these properties are affected by the degree of oxidation, the results show that bothNMR using a portable spectrometer and dielectric spectroscopy can be used as conditionmonitoring techniques to detect the degree of oxidation in complex systems such as filledcopolymers.

Access to energy is crucial for modern societies to function sustainably. In addition, nuclear power has for a long time been considered a reliable source of energy. However, the majority of nuclear power plants are reaching the end of their service lifetimes, and it is crucial to verify that every component can withstand the added service time. With the ability to monitor the condition of components and perform lifetime predictions, suitable maintenance and safe operations can be achieved.

The specific focus of this study was on ethylene-propylene diene (EPDM) rubber sealants with high filler content, which are replacing halogen-containing polymers. Two types of EPDM seals were studied: Lycron (Brattbergare), which is used in cable transit seal systems in reactor containment, and a carbon black-filled EPDM rubber sealant installed in a transportation valve for transporting old/spent nuclear fuel situated underwater in a reactor basin.

The changes that occur in EPDM cable transit seals during thermal ageing and the causes of these changes were investigated. Samples were tested at different temperatures between 110 °C and 170 °C and evaluated with respect to the distance from the surface via modulus profiling, infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The results showed the existence of three different deterioration mechanisms during ageing. By combining the different profile parameters, it was possible to quantify the contributing mechanism and to obtain information about the kinetics of the different processes. The effects of γ-irradiation on the EPDM cable transit seals in media with different oxygen partial pressures (1 – 21.2 kPa) were studied. By employing different profiling methods, it was possible to separate the mechanisms: polymer oxidation, migration of molar mass species and anaerobic changes in the polymer network. Additionally, the migration process during γ-irradiation was found to be accelerated for higher oxygen partial pressures. The effects of radiation on carbon black-filled EPDM seals in air and water were studied via irradiating samples at high dose rates (7 kGy/h) up to 3.5 MGy. This is the first study on the cross-sectional profiles of highly filled EPDM materials exposed to radiation in water, and it shows great differences in the chemical and physical properties of the material after irradiation in air and water. Of particular interest in this study were the use of a non-invasive portable NMR sensor (NMR-MOUSE) to acquire spatially resolved information from samples and the investigation of this promising method for onsite condition monitoring tests.

The effects of gamma radiation in air and water on a highly filled carbon-black-containing EPDM seal, used in transportation valves for old-fuel rods, were investigated. Samples were irradiated at a dose rate of 7 kGy h(-1) until total doses of 0.35, 1.4, 2.1 and 3.5 MGy were reached. The doses were chosen to correspond to 1, 4, 6 and 10 years of service. Infrared spectroscopy, mechanical indenter and NMR relaxation time (T-2) measurements indicated an oxidative crosslinking of the seal, which increased monotonically with the dose. The effects were larger in air than in water, and in air, diffusion-limited oxidation was observed. The compression set increased with increasing dose of radiation and was the highest for seals irradiated in air. The water uptake into the rubber, which was always lower than 1 wt.%, increased with the dose, showing the effect of increased polarity by the oxidation of the rubber.

The effects of γ-radiation in air and water on a highly filled carbon-black-containing EPDM seal, used in transportation valves for old-fuel rods, were investigated. Samples were irradiated at a dose rate of 7 kGy/h until total doses of 0.35, 1.4, 2.1 and 3.5 MGy were reached. The doses were chosen to correspond to 1, 4, 6 and 10 years in service. Infrared spectroscopy, mechanical indenter and NMR relaxation time (T2) measurements indicated an oxidative crosslinking of the seal, which increased monotonically with the dose. The effects were larger in air than in water, and in air, diffusion-limited oxidation was observed. The compression set increased with increasing doses of radiation and was the highest for seals irradiated in air. The water uptake into the rubber, which was always lower than 1 wt%, increased with the dose, showing the effects of increased polarity/oxidation of the rubber.

10.

Pourmand, Payam

et al.

KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Chemistry.

Hedenqvist, Mikael S.

KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.

Furo, Istvan

KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Chemistry.

Gedde, Ulf W

KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.

The effects of air ageing at different temperatures between 110 and 170 degrees C on cable transit seals based on highly filled EPDM rubber used in nuclear power plants were studied. The changes of the macroscopic mechanical properties (Young's modulus, indentation modulus and strain-at-break) were in accordance with the Arrhenius equation with an activation energy of 110 kJ mol(-1). Profiling to assess the structure and property gradients within aged blocks was performed via IR spectroscopy, micro-indentation, gravimetric analysis of n-heptane-extracted samples and non-invasive portable NMR spectroscopy. A previously developed methodology was used to separate the deterioration into three different processes: polymer oxidation that was diffusion-limited at all temperatures, migration of low-molar-mass species to the surrounding media and anaerobic changes to the polymer network. The methodology allowed the assessment of the kinetics (rate as a function of time and temperature) of the different processes. It was noticed that polymer oxidation yielded more crosslinking at higher temperatures than at lower temperatures. The data obtained by both the portable NMR (a non-invasive method) and the indentation modulus profiling showed correlations with strain-at-break data, indicating their usefulness as condition monitoring methods.

Highly filled EPDM rubber used in cable transit seals in nuclear power plants were exposed to gamma radiation at a high dose rate at 23 degrees C in media with different oxygen partial pressures (1-21.2 kPa). The motivation of this study was threefold: highly filled polymers are replacing halogen-containing polymers and these materials have rendered less attention in the literature; there is a need to find efficient tools to make possible condition monitoring and extrapolation. Several profiling methods were used: IR microscopy, micro-indentation, micro-sample extraction/gravimetry and non-invasive NMR spectroscopy, and three different deterioration processes were identified: polymer oxidation, migration of low molar mass species, and anaerobic changes in the polymer network. IR microscopy, micro-indentation profiling and the portable NMR method confirmed diffusion-limited oxidation in samples irradiated in air. The inner non-oxidized part of the blocks showed a pronounced change in the indenter modulus by migration of primarily glyceryl tristearate migration was accelerated by the presence of oxygen in the surface layer and anaerobic changes in the polymer network. For extrapolation or for condition monitoring, it is best to use the data obtained by indenter modulus profiling and to use the correlation between indenter modulus and strain-at-break to quantify the sample status. Non-invasive NMR profiling provided useful data but was less precise than the indenter modulus data to predict the strain-at-break.

The effects of thermal ageing on EPDM cable transit seals were investigated. Samples were aged in air at 110, 120, 150 and 170 °C, and evaluated with tensile testing, indenter modulus profiling, oxidation profiling (using IR spectroscopy), nuclear magnetic resonance (NMR) spectroscopy profiling. The ageing resulted in an increase in the indenter modulus, the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. Diffusion-limited oxidation (DLO) occurred with a large oxidation gradient close to the sample surface. The portable NMR MOUSE (non-invasive method) was used to obtain detailed degradation profiles, up to a depth of 5 mm of the aged samples. The results indicated a deterioration process that was attributed to several mechanisms, i.e. oxidation, anaerobic crosslinking and migration of oil extender. By combining the data acquired from the profiling, separation and quantification of these three contributing mechanisms was determined. Additionally, it was shown that the portable NMR data correlated well with the strain at break data, highlighting the potential use of the portable NMR for condition monitoring.

The changes occurring in EPDM cable transit seals during thermal ageing and the causes of these changes were investigated. Samples were aged at a temperature of 170 °C, and subsequently evaluated with respect to the distance from the surface with modulus profiling, infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, based on the extractable mass fraction profiles for initial and aged materials. The ageing resulted in an increase in the modulus and in the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. The NMR data were obtained in a non-invasive manner by ex situ experiments performed with a portable low-field spectrometer (NMR MOUSE). The results showed deterioration processes that can be attributed to different mechanisms i.e. oxidation, anaerobic crosslinking and migration of oil extender. The unique combination of parameter profiles made it possible to resolve and quantify these three contributing mechanisms. The NMR results highlight the potential of this method for on-site testing.

We have evaluated the potential of nuclear magnetic resonance (NMR) spectroscopy based on small portable magnets for in situ assessment of moisture protective properties of wood coatings. Low field (1)H NMR with a unilateral permanent magnet was used to monitor and map the local moisture content (MC) of wood specimens uncoated or coated with various types of commercial paint systems. The MC beneath a coating layer was measured with a penetration depth up to 5 mm and with a depth resolution of 0.2 mm. The method is quick, noninvasive, simple to perform, and does not require removing wooden parts from the structure.